1. Field of the Invention
The present invention relates generally to a process for producing hydrogen and, more particularly, to a process for producing high purity hydrogen from a specific hydrocarbonaceous feedstock.
2. Description of Background Art
There are a variety of known processes for producing hydrogen. Some of the more frequently employed processes include steam reforming of natural gas or naphtha, catalytic reforming of hydrocarbons boiling in the range of heavy straight run (HSR) gasoline or heavy oils (e.g., fuel oil), and the partial oxidation of heavy oils or natural gas. Steam reforming of natural gas is perhaps the most widely employed process for producing hydrogen. However, natural gas can contain certain sulphur species; typically hydrogen sulphide. Since reforming catalysts are extremely sulphur sensitive, the natural gas must undergo expensive pretreatment for sulphur removal, as is known by those skilled in the art.
To our knowledge, the use of the subject feedstock for the production of high purity hydrogen in a process which includes the sequence of steps described hereinbelow has, heretofore, never been offered. It is further believed that the instant method of producing pressurized, high purity hydrogen has also, heretofore, been unknown.
U.S. Pat. No. 3,545,926 describes a process for generating hydrogen from liquid hydrocarbons by partial oxidation followed by a water gas shift reaction and carbon dioxide removal.
U.S. Pat. No. 3,874,592 describes a burner for the partial oxidation of hydrocarbons to synthesis gas.
Commonly assigned U.S. patent application Ser. No. 614,335, filed Nov. 16, 1990, describes a process for producing high purity hydrogen from a refinery offgas feedstock. In particular, the process includes (1) partially oxidizing a refinery offgas feedstock to produce a synthesis gas mixture of carbon monoxide and hydrogen, (2) reacting said synthesis gas mixture with steam to convert said carbon monoxide into a raw gas mixture which primarily includes carbon dioxide and hydrogen, and (3) purifying said raw gas mixture to produce high purity hydrogen and a reject gas mixture of impurities.
U.S. Pat. No. 4,553,981 describes a process for hydrogen recovery from effluent gas streams. In particular, the effluent gas stream from steam reforming, partial oxidation or coal gasification operations are treated in shift conversion, scrubbing and pressure swing adsorption units for recovery of a purified hydrogen-containing product gas stream. After treatment by partial oxidation and high temperature shift conversion, the effluent stream typically has a composition, in mole percent on a dry basis, of 60-65 percent hydrogen and 30-35 percent carbon dioxide. The '981 patent teaches that a major portion (i.e., more than 70%, preferably 85-99.9%) of the carbon dioxide in the shift conversion effluent stream must be removed via scrubbing before being subjected to pressure swing adsorption for final purification. The high levels of carbon dioxide in the shift conversion effluent stream would result from charging a "heavy" hydrocarbon feed upstream to the partial oxidation unit.
Those skilled in the art certainly appreciate the economic disadvantages associated with a process for producing hydrogen that requires a scrubbing step. The space and costs relating to the installation and operation of the scrubber and equipment associated therewith, e.g., the conduits and refrigeration equipment, to name a few, result in a demand for a more economical approach. In fact, the scrubber and equipment associated therewith can constitute up to 50 percent of the total capital cost required to construct the processing equipment.
Accordingly, a process for producing high purity hydrogen which circumvents the need for practicing the expensive scrubbing step would be a significant contribution to those skilled in the art. In other words, this objective would be satisfied in a process where it is unnecessary to remove a major portion of carbon dioxide from the shift conversion effluent stream prior to subjecting said stream to purification by pressure swing adsorption.